1. Field of the Invention
The present invention relates to golf balls and more particularly, to such a golf ball that has a predetermined number of depressions on the surface of the core having at least one layer and the depressions have a predetermined total volume.
2. Description of the Related Art
In a conventional golf ball, the core is spherical and has a smooth surface. When a golf ball of this design is hit with a driver club, the ball is forced to spin at a high speed, shortening the ball carry and lowering the player's performance.
U.S. Pat. No. 698,516 discloses a three-piece golf ball in which the inner layer is made out of soft rubber, the intermediate layer is made out of gutta-percha and has depressions on the surface, and the outer layer is made out of celluloid. A golf ball of this design is durable in use. U.S. Pat. No. 712,413 discloses a three-piece golf ball in which the core is made out of soft rubber, the intermediate layer is made out of hard rubber and has fine through holes, and the cover is made out of tough rubber. A golf ball of this design has the characteristics of low cost and high durability. U.S. Pat. No. 5,836,834 discloses a three-piece golf ball comprising a two-layer solid core and a cover of ionomer resin, which encloses the two-layer solid core. The two-layer solid core consists of an inner core of low-hardness rubber and an outer core of high-hardness rubber disposed around the inner core with a boundary surface therebetween, wherein a plurality of projections are formed on the inner surface of the outer core such that the projections extend along an approximate radial direction, a plurality of depressions corresponding to the projections are formed in the outer surface of the inner core, the inner core and the outer core joined together such that the projections are closely inserted into the depressions, and the projections and the depressions are uniformly arranged over the entire boundary surface between the inner core and the outer core. When hitting a ball of this design with a driver club, the player will get a relatively hard feel. When hitting a ball of this design with a short iron, the player will get a relatively soft feel. However, the specifications of the aforesaid patents do not describe the characteristics of the detail construction, amount and distribution of the depressions and the effect of the depressions relative to the spin rate.
U.S. Pat. Nos. 6,379,270 and 6,383,091 disclose a similar concept. According to these two patents, the golf ball comprises a solid core, an intermediate layer, and a cover. The solid core or the cover is provided with a plurality of protrusions penetrating into the intermediate layer. The Shore D hardness value of the protrusions is greater than the intermediate layer. When the ball is driven with a driver club, the protrusions are forced to bend, resulting in a great amount of deformation of the ball, and therefore the spin rate of the ball is reduced and the flight performance is improved. When hitting the ball with a short iron, the protrusions do not bend and the amount of deformation of the ball is insignificant, and therefore the protrusions do not cause reduction of the spin rate and the flight of the ball is well controlled.
According to Table 3 of the specifications of U.S. Pat. Nos. 6,379,270 and 6,383,091, the number of the protrusions is more than one hundred, and their maximum cross-sectional size is 0.5 to 2.5 mm. During fabrication, it is difficult to strip off the core from the mold, resulting in low production efficiency and low yield rate. Further, when designing the ball, the designer must take the length and the pitch of the arrangement of the protrusions into account, preventing interference among protrusions and lowering the effect of the protrusions on the spin rate. These factors complicate the ball design.
Therefore, it is desirable to provide a golf ball that eliminates the aforesaid drawbacks.